Calorimetric low temperature detectors for low-energetic heavy ions and their application in accelerator mass spectrometry

Abstract

The energy-sensitive detection of heavy ions with calorimetric low temperature detectors was investigated in the energy range of E=0.1-1 MeV/amu, commonly used for accelerator mass spectrometry (AMS). The detectors used consist of sapphire absorbers and superconducting aluminum transition edge thermometers operated at T approximately 1.5 K. They were irradiated with various ion beams (13C, 197Au, 238U) provided by the VERA tandem accelerator in Vienna, Austria. The relative energy resolution obtained was DeltaE/E=(5-9) x 10(-3), even for the heaviest ions such as 238U. In addition, no evidence for a pulse height defect was observed. This performance allowed for the first time to apply a calorimetric low temperature detector in an AMS experiment. The aim was to precisely determine the isotope ratio of 236U/238U for several samples of natural uranium, 236U being known as a sensitive monitor for neutron fluxes. Replacing a conventionally used detection system at VERA by the calorimetric detector enabled to substantially reduce background from neighboring isotopes and to increase the detection efficiency. Due to the high sensitivity achieved, a value of 236U/238U=6.1 x 10(-12) could be obtained, representing the smallest 236U/238U ratio measured at the time. In addition, we contributed to establishing an improved material standard of 236U/238U, which can be used as a reference for future AMS measurements.

Application of CLTD’s for High Resolution Mass Identification and for Stopping Power Measurements of Heavy Ions

“…To operate the array, a windowless pumped 4 He-bath cryostat is used. A detailed description of the CLTD design can be found in [4]. The ToF system consists of two Chevron-MCP-detectors in a distance of approximately 1 m. Both MCP-detectors are equipped with 4 µg/cm 2 thin carbon converter foils at a size of 12 × 9 mm 2 and 45°electrostatic mirrors.…”

“…CLTD's provide, as compared to conventional ionization detectors, due to their detection principle, substantial advantages in detector performance, such as energy resolution and energy linearity, etc. CLTD's have been frequently demonstrated to achieve an excellent relative energy resolution of E/E = 1 − 2 × 10 −3 , and a good energy linearity with a complete absence of pulse-height defect, in a wide range of ions and energies [2,4]. Thus a combination of CLTD's as high-resolution energy detectors with ToF detectors provides a detector system for high-resolution mass identification of low energy heavy ions.…”

Application of Calorimetric Low Temperature Detectors (CLTD’s) for Precise Stopping Power Measurements of Heavy Ions in Matter

“…However, for high ion masses and low energies ionization based energy detectors, that are commonly used in experiments for stopping power determination [3,4], suffer from incomplete energy detection, resulting in pulse height defect and a relatively poor energy resolution. As CLTD's provide substantially better energy resolution and linearity for heavy ion detection, with the absence of any pulse height defect [5,6], this type of energy detectors has the potential to increase sensitivity and accuracy for dE/dx measurements and to extend the accessible energy range towards lower energies.For that purpose a CLTD array, that has been developed at GSI in the past years [5,6,7], has been used to replace the Si-detector in an established setup for dE/dx measurements at the K-130 cyclotron at the University of Jyväskylä [3,8], and to perform measurements with 0.05-1 MeV/u 131 Xe-ions in different absorber materials. As an example the measured electronic stopping power of Xe ions in carbon is displayed in fig.…”

“…However, for high ion masses and low energies ionization based energy detectors, that are commonly used in experiments for stopping power determination [3,4], suffer from incomplete energy detection, resulting in pulse height defect and a relatively poor energy resolution. As CLTD's provide substantially better energy resolution and linearity for heavy ion detection, with the absence of any pulse height defect [5,6], this type of energy detectors has the potential to increase sensitivity and accuracy for dE/dx measurements and to extend the accessible energy range towards lower energies.…”

“…For that purpose a CLTD array, that has been developed at GSI in the past years [5,6,7], has been used to replace the Si-detector in an established setup for dE/dx measurements at the K-130 cyclotron at the University of Jyväskylä [3,8], and to perform measurements with 0.05-1 MeV/u 131 Xe-ions in different absorber materials. As an example the measured electronic stopping power of Xe ions in carbon is displayed in fig.…”